Since the early 1980s, thousands of patients prone to irregular and sometimes life threatening heart rhythms have had miniature heart-monitoring devices, such as defibrillators, pacemakers, and cardioverters, implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to their hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.
The typical implantable heart-monitoring device includes a set of electrical leads, which extend from a sealed housing for implantation into the inner walls of a heart. The housing itself is typically somewhat flat and rectangular with rounded edges and corners to reduce stress on surrounding tissues after implantation. Within the housing are a battery for supplying power, heart-monitoring circuitry for monitoring the heart and detecting abnormal rhythmic conditions, and two or more capacitors for delivering bursts of electric current through the leads to the heart.
In many instances, each capacitor takes the form of a flat aluminum electrolytic capacitor. This type of capacitor generally includes a vertical stack of several flat D-shaped capacitor elements, or modules, with each module comprising at least one D-shaped paper separator sandwiched between D-shaped sheets of aluminum foil. The capacitor modules are electrically coupled together to provide a total capacitance and then housed in a D-shaped case made of aluminum or another metal compatible with the foil.
The aluminum case, which conforms closely to the shape of the vertical stack of D-shaped capacitor modules, has vertical sidewalls that are parallel to the vertical faces of the stack. The case also has D-shaped top and bottom portions that meet its vertical sidewalls to form approximate right-angle joints and corners along its top and bottom edges.
Two or more such capacitors are sometimes stacked on top of each other within the housing of an implantable device. When stacked, the walls of the D-shaped capacitors are aligned with each other, effectively forming a single vertical wall the combined height of the capacitors.
One problem with these types of flat capacitors and their stacked arrangement in implantable device housings is that the walls of the cases are incompatible with the rounded edges and corners of implantable device housings. Juxtaposing these vertical walls and right-angle corners against the rounded interior portions of the housings inevitably leaves gaps or voids between the cases and housings. These voids not only waste space, but ultimately force patients to endure implantable devices with larger housings than otherwise necessary.
Accordingly, there is a need for flat capacitors that better conform to the rounded portions of implantable medical-device housings.